Healthy leaves, no bugs? Mutation and or deformity. Kinda looks almost exactly! like what I saw very recently with my Northern lights #2 in veg. Weird right? Anyways, it's highly likely it's a harmless mutation and please don't worry about it, but I'd advise just watching her as you enter flower, just in case the mutation becomes more then a couple spindly, deformed leaves. My NL did this on only one side only, while the other side was perfectly fine, and did so 3 times at 3 new node points before it stopped and started to grow NORMAL fans again. I was worried about her and what this meant, but it's proven to be nothing at all. In third week of flower now and there hasn't been anything else. I also have a mutation with my Blue Cookies that comes around at least once a week, affecting only 2 or three fan blades at a time.... Again, it's weird but harmless. If you'd like to see the NL #2 I'm talking about and the foliage mutations I'm seeing on my BC just pop by my page and go to week 4. Blue cookies you can see the mutation on leaves in week 10/11.
You're good my friend, no worries. An oddity for sure, but it's highly unlikely this will have any consequence's. Good luck in the coming days๐๐